The present invention relates to a push button switch intended for use as a zooming switch in a camera such as a video camera, 8 mm camera, or the like. In such a switch, the resistance value of a pressure-sensitive resistance element contained in the push button switch is varied according to the depression pressure exerted on the push button. The rotational speed of a motor driving a zoom lens system, for instance, can thus be varied continuously with such a zooming switch.
FIG. 1 is a diagram showing a cross-sectional view of a conventional push button switch having a pressure-sensitive conductive rubber element 1 as a pressure-sensitive resistance element, an insulated push button 2, and a conductive layer 3. The pressure-sensitive conductive rubber element 1 is laminated through the conductive layer 3 to the insulated push button 2 as shown in FIG. 1. The pressure-sensitive conductive rubber element 1 is obtained by stamping a pressure-sensitive conductive rubber sheet so as to cut out the element 1 in the same shape as that of a pressing surface 2a of the push button 2.
Upon depressing the push button 2, the pressure-sensitive conductive rubber element 1 is pressed toward electrode patterns 14 and 15 formed on a substrate 4, as a result of which the electrodes 14 and 15 are electrically connected through the conductive layer 3. In this case, the resistance value of the conductive layer 3 varies in response to the pressure of the push button 2.
With such a push button switch as described above with reference to FIG. 1, the insulated push button 2 and the conductive layer 3 are molded together as a unitary member. Then, the pressure-sensitive conductive rubber element 1, which is stamped out in the desired shape from a pressure-sensitive conductive rubber sheet, is fixed to the conductive layer 3.
The conventional push button switch, however, is disadvantageous in that:
(i) the pressure-sensitive conductive rubber sheet is quite expensive; PA0 (ii) the manufacturing process is troublesome because the pressure-sensitive conductive rubber element has to be fixed to the conductive layer after the molding of the insulated push button 2 and the conductive plate 3; and PA0 (iii) it is necessary to provide various kinds of sensitive conductive rubber elements having various thicknesses in advance in order to be able to change the characteristics of the switch, i.e., the relationship between the pressure applied to the switch and resistance thereof. PA0 (1) A conductive rubber sheet coated with a pressure-sensitive conductive paste is stamped out to a desired shape by a pressing machine or, alternatively, a conductive rubber sheet stamped out to a desired shape by a pressing machine is coated with a pressure-sensitive conductive paste. PA0 (2) The stamped conductive plate coated with the paste and an insulated push button made from insulating rubber are molded together into a unitary piece by heat curing. PA0 (3) The push button is mounted above the electrode patterns.